HIGH-RESOLUTION TRANSMISSION ELECTRON-MICROSCOPY STUDY OF GOLD PARTICLES (GREATER THAN 1 NM), EPITAXIALLY GROWN ON CLEAN MGO MICROCUBES

Gold particles (greater than 1 nm) were vaccum deposited on clean surfaces of MgO microcubes in situ synthesized in a controlled atmosphere. The particles were observed simultaneously with the MgO substrate in plan view and in cross-section by high-resolution transmission electron microscopy, microdiffraction and convergent-beam electron diffraction. The gold particles (less than 4 nm) had a f.c.c. structure and were perfectly accommodated with the substrate, leading to a lattice expansion of 2.9%. In this size range (1-4 nm), all the particles were single crystals and had an half-octahedron shape with (001) truncations on the edges. The interface between the particles and the MgO substrate was flat; no defects were imaged. In contrast larger (greater than 4 nm) particles have the lattice parameter of the bulk material. The high stability of the particles in the electron beam was certainly due to their strong interaction with the clean MgO surface.